1. Field of the Invention
The present invention relates generally to a wireless communication system, and more particularly, to a data transmission method through a physical channel and a transmission chain therefor.
2. Discussion of the Related Art
In a certain wire/wireless communication system, a transmitter transmits one among various types of transmission formats over a specified physical channel. Nevertheless, if it is required for a receiver to receive the data over the channel without any information on the transmission format, the receiving end performs a blind format detection. As an example of such a system, there is the 1x-EVDV system
In the 1x-EVDV system, at least one of a plurality of forward packet data control channels (F-PDCCHs) may be used to transmit control information of a forward packet data channel (F-PDCH) that is a physical channel for transmitting packet data.
Specifically, for the packet data transmission, the conventional wireless communication systems use a physical channel, such as a packet data channel (PDCH), a packet data control channel (PDCCH), etc.
The PDCH is a channel that is used to transmit packet data to a corresponding terminal (or a user, hereinafter referred to as terminal).
The PDCCH contains control information for enabling the corresponding terminal to receive, without error, the packet data being transmitted through the PDCH.
The PDCCH is a forward channel that includes the control information on the PDCH. The receiver extracts the control information from the PDCCH, and decodes the PDCH using the control information.
Generally, the PDCCH is composed of various kinds of information required for decoding of 13˜21 bits, cyclic redundancy checking (CRC) bits of 6˜8 bits for checking existence/nonexistence of a receiving error of the information, and convolutional encoder tail bits of 8 bits.
The whole information of 27˜37 bits as constructed above is produced as coded bits of 54˜64 bits (in case of ½-coding) or coded bits of 108˜128 bits (in case of ¼-coding) by a convolutional encoder having a ½ or ¼ code rate.
Hereinafter, a conventional method of puncturing the coded bits will be explained with reference to the following drawings.
FIG. 1 is a block diagram of a transmission chain of a general F-PDCCH.
The data (i.e., input sequence) transmitted through a general F-PDCCH is combined with an error detection code, such as a CRC code, through an error detection code addition block 101 which consists of a single CRC generator.
Generally, a medium access control (MAC) identifier (MAC_ID) is the control information included in a service data unit (SDU) transferred from a MAC layer, and indicates an identifier of the terminal to which the corresponding SDU is to be transmitted. The error detection code addition block 101 generates an error detection code.
Tail bits for sending the final state of the encoder as a trellis termination state are added to the bits having the CRC code in a tail bit addition block 102.
The bits to which the tail bits are added is encoded using a convolutional code in an encoder 103.
Through the above-described process, the generated coded bits are repeated through a symbol repetition block 104 to match the length of a transmission slot, and the repeated bits are punctured in a puncturing block 105.
For instance, since the number of usable Walsh codes is limited in the 1x-EVDV system, a Walsh code having a length of 64 chips is used for the PDCCH. Thus, the number of coded bits included in one slot is 48.
The slot length used to transmit the PDCCH is classified into one slot, two slots, and four slots. For example, the 48 coded bits are included in one slot, 96 coded bits are included in two slots, and 192 coded bits are included in four slots.
For instance, as shown in FIG. 1, if 8-bit CRC bits and 8-bit encoder tail bits are added to the 18-bit information bits, and a channel code having a ½ code rate is used for the transmission of one slot, 68 coded bits are generated. Then, the generated coded bits are punctured through the puncturing block 105 to match the length of the transmission slot.
Since one slot is for transmitting 48 coded bits, the puncturing of 20 (i.e., 68−48=20) bits is performed, and then 48 coded bits are transmitted through the one slot.
At this time, if the same amount of information is transmitted through four slots, the corresponding information bits, as shown in FIG. 1, are generated as 136 coded bits through an encoder having a ¼ code rate, and then generated as 272 bits through a symbol repetition block. Since these 272 bits should be transmitted through four slots, i.e., 192 bits, 80 (=272−192) bits are punctured. These 192 bits are transmitted, being equally divided into four slots.
The punctured bits are interleaved through a block interleaver 106, and then modulated by a modulator 107 in accordance with a QPSK method. The modulated signal is divided into an I-channel signal and a Q-channel signal using a portion of Walsh codes.
As described above, the transmission length of the F-PDCCH may be one slot, two slots, or four slots. Here, the slot means a time unit of 1.25 msec. At this time, the transmitter does not inform the length of the F-PDCCH currently being transmitted to the receiver. In other words, the receiver does not accurately know what format is being received. Accordingly, the receiver performs the decoding process with respect to three formats (i.e., three lengths of one slot, two slots, and four slots) and checks the CRC to detect what is the transmission length (or format) of the received F-PDCCH.
As described above, in case that the receiver determines the format of the transmission channel only using the CRC, a case that the CRC has the same value of ‘1’ (which corresponds to the case that an accurate transmission format is detected) may occur with respect to two or more kinds of formats. In this case, the receiver cannot accurately determine what kind of transmission format is transmitted through the channel. Accordingly, an additional device for minimizing the occurrence of such a case is required.